The invention relates to a method and an apparatus for forming stacks of printed products supplied in an overlapping flow which is conveyed continuously in the direction of a stacking shaft.
With fast-moving apparatuses of the aforementioned type, the overlapping flow that is conveyed on an endless conveyor is normally slowed down or even stopped to generate a gap between two printed products. An intermediate element is inserted into this gap in the stacking shaft, and a partial stack is then formed thereon with the following printed products. Solutions for forming such a gap are known for which the overlapping flow must be accelerated in its downstream region or for which upstream sections of the overlapping flow are slowed down and downstream sections are accelerated.
Speed changes of this type will cause erratic behavior of the overlapping flow, which can make the stacking operation more difficult or can even interrupt it. This can result in changes in the overlapping length, even resulting in a negative overlapping, as well as an offset on the side. This can even cause a slanted positioning and damage to single or multiple printed products in the partial stack and can furthermore cause problems during the forming of the main stack.
With other known apparatuses, the overlapping flow is supplied continuously to the stacking shaft, wherein the stacks formed in this way are only separated later on. However, the respective method cannot be automated at a justifiable expense.
An apparatus for arranging printed products in vertical partial stacks is disclosed in German patent document DE 19855510 A1. For this, two support fingers of a separating device, which are arranged on both sides of the stacking shaft, move into the region of the stacking shaft. The support fingers are pushed between two successively following printed products of the overlapping flow, thereby preventing the dropping of the following printed product. As a result of this delay in the overlapping flow, the stack support which takes the form of two rakes arranged on either side of the stacking shaft, can be inserted into the gap between the dropping printed products and can thus accommodate a partial stack that forms. The disadvantage of such an arrangement is that printed products can be speared or not cleanly separated during the insertion of the support fingers, which can then result in malfunctions and operational stops for the total system.
Another apparatus disclosed in German patent document DE 19947329 A1 is used to form a vertical stack with printed products supplied in an overlapping flow by a conveyor belt and to discharge these in the form of a desired number of partial stacks. This apparatus is provided with a first support finger, arranged on the side of the stacking shaft that is facing away from the conveyor belt. The support finger is moved vertically from a starting position, in which the finger projects above the overlapping flow into the center of the stacking shaft, to an end position where it projects into the overlapping flow. The printed products, which are conveyed into the stacking shaft after the first support finger assumes the end position, are thus deposited so as to form a partial stack on the support finger. A second support finger, arranged on the side of the stacking shaft that is facing the conveyor belt, is also inserted into the stacking shaft and, together with the first support finger, functions to support the partial stack, and to separate this partial stack from the previous partial stack or from the main stack. Once the support fingers have moved horizontally out of the stacking shaft, the printed products in the partial stack drop onto the stack support inside the stacking shaft to form a main stack. An arrangement of this type has the disadvantage that with high speeds for supplying the overlapping flow, thin printed products can be deformed and damaged by the support fingers or that during the intermediate storage, they can project on both sides of the respective support finger far below the horizontal line into the stacking shaft and can therefore drop deformed into the shaft. In turn, this can lead to malfunctions and stopping times for the total system.
With separating devices which are arranged on the conveyor belt side that is facing away from the stacking shaft and, in particular, are embodied as rakes and are operated at high speeds, it is possible when processing thin or large-surface printed products that the first product following the location of separation from the rake is gripped so that it is positioned in part above and in part below the finger of the rake and can also be damaged. Since a printed product, which is jammed in this way, cannot be removed automatically during the normal production process, the complete system must be shut down.